1. Field of the Invention
In general, the invention relates to methods for beat synchronization between media assets, and, more particularly, to the automated creation of beat synchronized media mixes.
2. Description of the Related Art
In recent years, there has been a proliferation of digital media players (i.e., media players capable of playing digital audio and video files.) Digital media players include a wide variety of devices, for example, portable devices, such as MP3 players or mobile phones, personal computers, PDAs, cable and satellite set-top boxes, and others. One example of a portable digital music player is the iPod® manufactured by Apple Inc. of Cupertino, Calif.
Typically, digital media players hold digital media assets (i.e., media files) in internal memory (e.g., flash memory or hard drives) or receive them via streaming from a server. These media assets are then played on the digital media player according to a scheme set by the user or a default scheme set by the manufacturer of the digital media player or streaming music service. For instance, a media player might play media assets in random order, alphabetical order, or based on an arrangement set by an artist or record company (i.e., the order of media assets on a CD). Additionally, many media players are capable of playing media assets based on a media playlist. Media playlists are usually generated by a user, either manually or according to a set of user-input criteria such as genre or artist name.
Digital media assets can be any of a wide variety of file types, including but not limited to: MPEG-1 Layer 2, MPEG-1 Layer 3 (MP3), MPEG-AAC, WMA, Dolby AC-3, Ogg Vorbis, and others. Typically, media assets that have been arranged in media playlists are played with a gap between the media assets. Occasionally, more sophisticated media playing software will mix two media assets together with a rudimentary algorithm that causes the currently playing media asset to fade out (i.e., decrease in volume) while fading in (i.e., increasing in volume) the next media asset. One example of media playing software that includes rudimentary mixing between subsequent media assets is iTunes® manufactured by Apple Inc. of Cupertino, Calif.
However, there is a demand for more sophisticated mixing techniques between media assets than is currently available. For instance, no currently available media playing software is capable of automatically synchronizing the beats between two or more media assets.
Beat synchronization is a technique used by disc jockeys (DJs) to keep a constant tempo throughout a set of music. Beat synchronization is accomplished in two steps: beatmatching (adjusting the tempo of one song to the tempo of another) and beatmixing (lining up the beats of two beatmatched songs.)
Originally, beatmatching was accomplished by counting the beats in a song and averaging them over time. Once the tempo of the song (expressed in beats per minute (BPM)), was determined, other songs with the same tempo could be strung together to create a music set. In response to a demand for more flexibility in creating their music sets, record players (also known as turntables) with highly adjustable speed controls were employed. These adjustable turntables allowed the DJ to adjust the tempo of the music they were playing. Thus, a DJ would play a song with a particular tempo, and adjust the tempo of the next song such that the two songs could be seamlessly beatmixed together. A DJ would use headphones, a sound mixer, and two turntables create a ‘set’ of music by aligning the beats of subsequent songs and fading each song into the next without disrupting the tempo of the music. Currently, manually beatmatching and beatmixing to create a beat-synchronized music mix is regarded as a basic technique among DJs in electronic and other dance music genres.
However, dance club patrons are not the only people who value beat-synchronized music mixes. Currently, many aerobics and fitness instructors use prepared beat-synchronized music mixes to motivate their clients to exercise at a particular intensity throughout a workout. Unfortunately, using the techniques of beatmatching and beatmixing to create a beat-synchronized music mix requires a great deal of time, preparation, and skill, as well as sophisticated equipment or software. Thus, music lovers wishing to experience a dance club quality music mix must attend a dance club or obtain mixes prepared by DJs. In the case of fitness instructors who want to use beat-synchronized music mixes, rudimentary DJ skills must be learned or previously prepared beat-synchronized music mixes must be purchased to play during their workouts.
Currently, even in the unlikely event that a consumer is able to obtain a pre-selected group of beatmatched media assets (i.e., each media asset has the same tempo as the rest) from a media provider, the transitions between media assets are not likely to be beat-synchronized when played. This is because current media players lack the capability to beatmix songs together. Further, even if a group of songs has the same average tempo, it is very likely that at least some beatmatching will have to be performed before beatmixing can occur. Thus, there is a demand for techniques for both automated beatmatching and automated beatmixing of media.
Even professional DJs and others who desire to put together beat-synchronized mixes often have to rely on their own measurements of tempo for determining which songs might be appropriate for creating a beat-synchronized mix. In some instances, the tempo of a song might be stored in the metadata (e.g., the ID3 tags in many types of media assets), but this is by no means common. Thus there is a demand for automated processing of a collection of media assets to determine the tempo of each media asset.
It should be noted that, even in electronic music, which often has computer generated rhythm tracks, the tempo is often not uniform throughout the track. Thus, it is common for music to speed up and/or slow down throughout the music track. This technique is used, for example, to alter mood, to signal a transition to a song chorus, or to build or decrease the perceived intensity of the music. This effect is even more pronounced in non-electronic music, where the beat is provided by musicians rather than computers, and who may vary the speed of their performances for aesthetic or other reasons. For example, it common practice for a song to slow down as it ends, signaling to the listener that the song is over. Speed variations may be very subtle and not easily perceptible to human ears, but can be significant when creating a beat-synchronized music mix. Thus, conventional tempo measuring techniques which output a single number to represent the tempo of the track actually output an average BPM, which can be misleading to someone who is looking for a song segment (such as the beginning or end of a song) with a particular tempo. Thus there is a demand for more complete descriptions of tempo throughout a media asset.
Further still, not everyone who wants a beat-synchronized music mix is knowledgeable or interested enough to use tempo as a criterion for selecting media. Thus, there is a demand for creating a beat-synchronized music mix based on other, subjective or objective criteria, for example, the perceived intensity or genre of the music.
Accordingly, there is a demand for new methods for automatically selecting music or other media for and creating beat-synchronized media mixes. Further, there is a demand for the creation of a beat-profile for any given media asset, as opposed to conventional average tempo measurements.